Format number as phone in text box when onBlur

I’m terrible at JS regular expressions and I’m counting on an intelligent being to help me accomplish what should be a trivial task.

Onblur, I want a text field of 10 numbers ‘1234567890’ to be formatted as 123/456/7890 using JS.

And Onfocus, it should revert to the number ‘1234567890’ without slashes.

That’s it. Hope you can help!

Update: I arrived at a solution, so I’ll post the answer below for the sake of future searchers.

HTML:

<input id="PhoneNumber" type="text" maxlength="10"
       onblur="PhoneNumberOnBlur(this)"
       onfocus="PhoneNumberOnFocus(this)"/>

Javascript:

function PhoneNumberOnBlur(el) { el.value = el.value.replace(/(\d{3})(\d{3})(\d{4})/, "$1/$2/$3"); }

function PhoneNumberOnFocus(el) { el.value = el.value.replace(/\//g, "") }